We propose to clone, express, in vitro characterize and perform preclinical testing of two human monoclonal IgG1, kappa, antibodies, RF-1 and RF-2, that binds specifically and with high affinity to the fusion protein of the human Respiratory Syncytial Virus (RSV). The antibodies have in vitro virus neutralizing activity at concentration as low as 30 and 8 ng/ml, respectively. The antibodies have neutralized all virus strains tested, covering both subtypes A and B and wildtypes and laboratory strains. The antibodies do not cross-react to 4 human RSV negative cell lines, each representing different tissue types. We plan to clone the antibody coding genes and then insert them into a high efficiency CHO expression vector. Two forms of each antibody will be produced, a gamma1 and a gamma4 (PE) form. The antibodies will first be tested in vivo as gamma1 versions in a Balb/c model; the best performing will then be tested as a gamma4 (PE) version. The best antibody will then be tested for cross-reactivity to human tissues. The second animal model, the African green monkey, will be used to assess the efficacy of the antibody in preventing lung damage by RSV. In both animal models, the antibody(ies) will be tested for prophylactic and therapeutic efficacy, and for its effect on the animals response to RSV. PROPOSED COMMERCIAL APPLICATION: approximately 90,000 people are hospitalized each year due to RSV infectious; of these, a majority will suffer lifelong pulmonary problems and approximately 4,500 subsequently die. These patients are the core target population with a therapeutic aim. It is expected that a larger target population of approximately 200,000 subsequently could become applicable for prophylactic treatment. Polyclonal antibody preparations have shown efficacy in prophylacsis and therapy of RSV infection. A monoclonal antibody would have several advantages over such a polyclonal preparation including: consistency, higher effect/dose, ease of production and no possibility for concomitant viral contamination.